The need to store digital files, documents, pictures, images and other data continues to increase rapidly. In connection with the electronic storage of data, various data storage systems have been devised for the rapid and secure storage of large amounts of data. Such systems may include one or a plurality of storage devices that are used in a coordinated fashion. Systems in which data can be distributed across multiple storage devices such that data will not be irretrievably lost if one of the storage devices (or in some cases, more than one storage device) fails are also available. Systems that coordinate operation of a number of individual storage devices can also provide improved data access and/or storage times. Examples of systems that can provide such advantages can be found in the various RAID (redundant array of independent disks) levels that have been developed. Whether implemented using one or a plurality of storage devices, the storage provided by a data storage system can be treated as one or more storage volumes.
In order to facilitate the availability of desired data, it is often advantageous to maintain different versions of a data storage volume. Indeed, data storage systems are available that can provide at least limited data archiving through backup facilities and/or snapshot facilities. The use of snapshot facilities greatly reduces the amount of storage space required for archiving large amounts of data. However, there are still times where it is desirable to delete a snapshot to conserve storage space.
Current processes employed to delete snapshots are efficient enough at independently deleting such snapshots. When a snapshot is deleted a number of different tasks need to be performed to ensure that artifacts from the deleted snapshot do not remain thereby disrupting or possibly corrupting subsequent snapshots. The deletion of a single snapshot may take up to a couple of seconds or more before it is completely deleted.
A drawback to some snapshot facilities is that only one snapshot, or sometimes one snapshot per backing store, may be deleted at a time. As used herein, a “backing store”, which may also be referred to as a snap pool, is a storage location where all snapshot related data and metadata is recorded. Accordingly, when more than one snapshot is marked for deletion a delete queue has to be formed. While a snapshot is in the process of being deleted all other snapshots that are marked for deletion remain in the delete queue. In the event that a large number of snapshots are marked for deletion, for example after a rollback process has been performed in response to data corruption on a master volume, the act of incrementally deleting each snapshot marked for deletion may take a relatively long time. Meanwhile, storage resources are occupied by snapshots awaiting their turn for deletion. The net result is that the storage resources cannot be allocated for maintaining data for current snapshots until the resources occupied by deleted snapshots are processed and freed. This may cause some amount of frustration for a user that has to wait until all resources corresponding to deleted snapshots are freed before the user can create a new snapshot of the master volume. Although the user is not able to see how the resources are allocated and it appears as though the snapshots are already deleted, these restrictions nevertheless may cause the user frustration if they have to wait to create a new snapshot.